/Engine/Source/Runtime/RenderCore/Public/RenderGraphBuilder.h
A variant of CreateBuffer where users supply NumElements through a callback. This allows creating buffers with sizes unknown at creation time. The callback is called before executing the most recent RDG pass that references the buffer so data must be ready before that.
FRDGBufferRef CreateBuffer ( const [FRDGBufferDesc](API\Runtime\RenderCore\FRDGBufferDesc) & Desc, const TCHAR * Name, FRDGBufferNumElementsCallback && NumElementsCallback, ERDGBufferFlags Flags )